Soleus H reflex and motor unit number estimation after tibial nerve block and neurotomy in patients with spastic equinus foot.

OBJECTIVE

To assess and compare, clinically and electrophysiologically, the effects on muscle innervation and spasticity of selective anaesthetic nerve block and selective neurotomy of the motor-nerve branch to the soleus muscle in patients with spastic equinus foot.

METHODS

Eleven hemiplegic patients were studied before and after anaesthetic tibial-nerve block, and at two months and one year after tibial nerve neurotomy. Triceps surae spasticity and strength, walking speed, gait kinematics of the ankle, maximal amplitude of the H reflex and of the M-response and the Hmax/Mmax ratio of the soleus muscle, and the mean motor unit action potential area and motor unit number estimation (MUNE) of the soleus muscle were calculated on the normal and spastic side.

RESULTS

Spasticity and equinovarus improved in a similar fashion after tibial nerve block and neurotomy. The soleus Hmax/Mmax ratio decreased by 42% after tibial nerve block and 77% after neurotomy. The soleus MUNE decreased by 52% after tibial nerve block and by 86% after neurotomy.

CONCLUSION

Diagnostic nerve block predicts the spasticity and gait improvement, which is expected after neurotomy. The clinical improvement was similar after block and neurotomy. Nerve block is associated with a 50% decrease in the soleus Hmax/Mmax ratio and soleus MUNE. The median 80% neurotomy is associated with an 80% decrease in the soleus Hmax/Mmax ratio and soleus MUNE.